Initializes prefetch on external subtitle track activation, detects
seeks via time-pos delta threshold, pauses prefetch during live
subtitle processing, and restarts on cache invalidation.
- Extract loadSubtitleSourceText into reusable function
- Add prefetch service state and initSubtitlePrefetch helper
- Thread onTimePosUpdate through event actions/bindings/main-deps
- Pause prefetch on subtitle change, resume on emit
- Restart prefetch after tokenization cache invalidation
- Query track-list on media path change to find external subs
- Stats server auto-start on immersion tracker init
- Stats overlay toggle via keybinding and IPC
- Stats CLI command (subminer stats) with cleanup mode
- mpv plugin menu integration for stats toggle
- CLI args for --stats, --stats-cleanup, --stats-response-path
- show a dedicated startup OSD "building" phase for character dictionary sync
- forward bare `Tab` from visible overlay to mpv so AniSkip works while focused
- fix Windows plugin env override resolution for `SUBMINER_BINARY_PATH`
- Add default `f` fullscreen overlay binding and switch default AniSkip skip key to `Tab`
- Make character-dictionary auto-sync non-blocking at startup with tokenization gating for Yomitan mutations
- Add ordered startup OSD progress (checking/generating/updating/importing), refresh current subtitle on sync completion, and extend regression tests
